gbefb: fix section mismatch warnings

Make 'default_mode' and 'default_var' be __initdata.
Fixes these section warnings:

WARNING: vmlinux.o(.data+0x128e0): Section mismatch: reference to .init.data:default_mode_CRT (between 'default_mode' and 'default_var')
WARNING: vmlinux.o(.data+0x128e4): Section mismatch: reference to .init.data:default_var_CRT (between 'default_var' and 'dev_attr_size')

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>